The Da Vinci Notebooks at sacred-texts.com
The Germans are wont to annoy a garrison with the smoke of feathers, sulphur and realgar, and they make this smoke last 7 or 8 hours. Likewise the husks of wheat make a great and lasting smoke; and also dry dung; but this must be mixed with olive husks, that is olives pressed for oil and from which the oil has been extracted. 597
256:597 : There is with this passage a sketch of a round tower shrouded in smoke.